In general, the dynamic range is a ratio between a maximum and a minimum of a selected physical parameter, where the selected physical parameter depends on the type of data being measured. For a scene, the dynamic range is the ratio between the brightest and darkest parts of the scene. For an image sensor, on the other hand, the dynamic range typically is defined as is the ratio of the intensity that just saturates the image sensor to the intensity that just lifts the image sensor response one standard deviation above camera noise.
The image sensors of most commercially available cameras cannot capture the full dynamic range of a scene. For this reason, images that are acquired by such cameras from a scene containing large variations in light intensity typically fail to capture all the detail of the scene. For example, high luminosity regions of the scene tend to appear uniformly bright and saturated in the acquired images and low luminosity regions of the scene tend to appear uniformly dark in the acquired images.
Many proposals have been made for increasing the dynamic range of images of a scene. Many recent approaches involve combining images of a scene that were acquired at different exposure levels to produce a final image having a higher dynamic range than the constituent images. The multiple exposure constituent images of the scene typically are acquired using a single camera at different capture times. As a result, the corresponding elements of the scene that appear in these images typically are not aligned because of motion of the camera or dynamic elements of the scene. To compensate for such motion-induced misalignment, the constituent images typically are warped to the coordinate system (or reference frame) of one of the constituent images that is designated as the reference image.
The warped images are fused together to produce a high dynamic range final images of the scene. The pixel values in the final image typically are determined from a weighted average of the values of the corresponding pixels of the constituent images. In some approaches, the weights are selected to downplay contributions from pixels of the non-reference ones of the constituent images that have significantly different radiance values than radiance values of the corresponding pixels of the designated reference image. Oftentimes, the fused images that are produced by these methods have visible artifacts, which are caused by inaccurate image alignment or the ways in which the contributions from the constituent multiple exposure images are combined into the fused images.
What are needed are systems and methods of combining multiple exposure images in ways that increase dynamic range while reducing blending artifacts in the final image.